Nice to support geometry stylesheets

[alshan]

I.e. geometry defaults: sizes, palettes etc., in addition to flavors. See Matplotlib stylesheets: https://matplotlib.org/stable/gallery/style_sheets/style_sheets_reference.html

Related concern:

I have been wondering if there is an easy way to get back to the default qualitative color palette and geometries size/line-width of the version 3.2 ?

https://github.com/JetBrains/lets-plot/issues/738#issuecomment-1888833493